Telephone system



April 14, 1942. T. F. cRocKER TELEPHONE SYSTEM Filed Nov. 18, 1940 6 Sheets-Sheet 1 THoMAs F. oRocKER' ATTORNEYS April 14, `1942- T. F. cRocKER TELEPHONE SYSTEM 6 Sheets-Sheet 2 Filed NOV. 18, 1,940

"/STF/BUTOR INVENTOR THOMAS F. CROCKER f BY ,oww .4457 M m 'ATTORNEYS April 14, 1942.- T F QRQCKER 2,279,448

` TELEPHONE SYSTEM Filed-Nov. 18, 1940 e sheets-sheet 5 FND 326 312 332 El? 300 HRST OPERATOR Pos/r/a/v INVENTOR THOMAS F.GROCKER ATTORNEYS April 14, 1942 T. F. cRocKER 2,279,448

TELEPHONE SYSTEM A'TToRNEYs April 14, 1942 T. r''. cRocKER 2,279,448 TELEPHONE SYSTEM y 'Filed Nov. 18, 1940 6 sheets-sheet e.

TONE APPR. 60,0

Ac. sfPPLYI v 660 366/ l L.. 652

` INVENTOR THOMAS F. GROCKER BY l TToRNEYs l Patented Apr. i4, i942 ,iis

ric

TELEPHONE SYSTEM Thomas F. Crocker, Chicago, Ill., assignor to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application November 18, 1940, Serial No. 366,127

24 Claims.

The present invention relates to telephone systems and more particularly to improved automatic switching apparatus of the character of that disclosed and claimed in U. S. Patent No. 2,070,874, John H. Voss and Thomas F. Crocker, granted February 16, 1937, which -apparatus is connected and arranged to handle switchboard traffic.

A telephone system of the character of that disclosed in lthe Voss and Crocker patent mentioned comprises a switchboard provided with a number of operator positions and a number of groups of switching links individually associated with the operator positions, each operator position comprising equipment operative to select for use any idle one of the switching links in the associated group. Each switching link includes an answer switch and a call switch, the answer switch of a selected switching link being operative to select a calling toll or trunk line accessible thereto and the call switch of a selected switching link being operative to select a called toll or trunk line accessible thereto. The operation of the answer switch of a selected switching link is controlled automatically by a distributor com monly associated with the groups of switching links; while the operation of the call switch of a selected switching link is under the control of the position equipment at the associated operator position.

In a telephone system of this character, the operator at an operator position at the switchboard frequently disconnects a switching link in use from the associated operator position after the operation of the call switch thereof has been controlled and prior to the complete operation of the call switch, particularly when the switching link is utilized to extend a connection to a local subscriber substantion.A This mode of operation of the equipment at the operator position in conjunction with the extension of connections to local subscriber substations is employed in view'of the fact that the connections are routed by way oi a local switch train, in which automatic ringing of the called subscriber substations is utilized.

While this mode of operation of the equipment at the operator position is very advantageous in that it appreciably facilitates rapid extension of calls to local subscriber substations, it does not permit of complete supervision of the completion of such connections. For example. when this Inode of operation of the equipment at the operator Vposition is employed and the called local subscriber substation is found to be :i

busy incident to the complete operation of the local switch train, the busy tone signal returned from the local switch train over the switching link in use to the calling line is not transmitted tothe associated operator position, the switching link in use being disconnected from the associated operator position at this time. Hence, the operator at the associated operator position is not advised of the noncompletion of the connection due to the busy condition mentioned.

Accordingly, it is an object of the present invention to provide in a telephone system of the character described, including an operator position and a link selectively connectable thereto,

. an improved arrangement for supervising connections extended over the link, regardless of whether the link isconnected to or disconnected from the operator position.

Another object of the invention is to provide in' a telephone system, including an operator position and an associated switching link operative to extend connections therefrom, an improved arrangement for selectively controlling the operation .of the switching link and for supervising connections extended thereover. A further object of the invention is to provide in a telephone system, including an operator position, an improved switching link associated with the operator position which embodies simple and positive control and supervisory facilities.

The invention is illustrated as being embodied in a telephone,l system comprising a central oilce of any suitable type, a private automatic branchv exchange or P. A. B. X., an intermediate branch exchange or I. B. X. of the automatic type and a distant exchange of any suitable type. A switchboard is arranged in the P. A. B. X. which comprises a number of operator positions. Further, a toll switch train is arranged in the P. A. B. X. which comprises a number of groups of switchinglinks individually associated with the operator positions, each switching link including an answer switch and a call switch, the toll switch train being utilized vto complete toll and trunk connections. Finally, a local switch train is arranged in the P. A. B. X., the local switch train being utilized to complete local connections in the P. A. B. X.

In accordance with one feature of the invent tion, the telephone system comprises a plurality of lines, an operator position, a link, means selectively contrcllable from the operator position for connecting the link to and for disconnecting the link from the operator position, means for connecting the link to a calling one of the lines,

the presence of the busy signal upon the link4V and governed only in the event the link is disconnected from the operator position for controlling the signal device.

In accordance with another feature of the invention, the link includes a voice current channel; and the busy signal is impressed by way of a high impedance path upon the channel of the link. Further, a tone detecting and amplifying arrangement is provided, which comprises an electric discharge device, including a space current path and a control electrode, means controlled in accordance with the resistance of the space current path for controlling the signal device, and means for amplifying the busy signal impressed upon the channel of the link and forimpressing the amplified busy signal upon the control electrode, thereby to control the resistance of the space current path.

In accordance with a further feature of the invention, the telephone system comprises, in addition to the means responsive to the connection of the link to a busy called line for controlling the signal device, means responsive to the connection of the link to an idle called line and governed only in the event the call on the idle called line is not answered within a predetermined time interval after the link is connected thereto for controlling the signal device.

In accordance with a further feature of the invention, the telephone system comprises a timer, rst and second intermittent signal voltages'having` different periodicities, means responsive to the connection of the link to a called line for operating the timer and for impressing either the first signal voltage or the second signal voltage upon the link, depending upon the idle or busy condition of the called line, apparatus operative through a` complete cycle to 4control the signal device, means governed jointly by the presence of either one of the signal voltages upon the link and the operation of the timer for initiating loperation of the apparatus, and means governed by the operation of the timer for arresting operation of the apparatus, whereby the apparatus is operated through a complete cycle of operation only in the event a predetermined one of the signal voltages is impressed upon the link. Furthenan arrangement is provided for preventing operation of the timer, in the. event the link is not disconnected from the associated operator position or in the event the link is connected to a called line of a particular class. Finally, the operation of the timer is arrested in the event the link is connected to an idle called line, when the call on the idle called line is answered.

Further features of the invention pertain to thel particular arrangement of the circuit elements of the system, whereby the above-outlined and additional operating. features are attained.

The novel features believed to be characteristicof the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which Figure 1 illustrates the general arrangement of a telephone system embodying the present invention; and Figs. 2 to 6, inclusive, taken together, and arranged in side-by-side relationship, illustrate the details of a system having incorporated therein the features of the invention, as briefly outlined above.

Description of the apparatus incorporated in the telephone system Referring now more particularly to Fig. 1 of the drawings, the telephone system there illustrated comprises a central ofce 20, a P. A. B. X. 30, an I. B. X. 40 and a distant exchange 50. The central office 20 and the distant exchange 50 are of any well-known type each serving a number of subscriber substations, not shown; while the P. A. B. X. 30 and the I. B. X. 40 are of the automatic typeA each serving a number of automatic subscriber substations, More particularly, the P. A. B. X. 30 serves a number of subscriber substations, including the subscriber substations T3 and T4; while the I. B. X. 40 serves a number of subscriber substations, including the subscriber substations TI and T2. The central oice 20 and theP. A. B. X. 30 are interconnected by a group of one-way trunk lines, including the trunk line 203 extending from the central oiice 20 to the P. A. B. X. 30, and a group of one-way trunk lines, including the trunk line 202 extending from the P. A. B. X. 30 to the central office 20. The I. B. X. 40 and the P. A. B. X. 30 are interconnected by a group of twoway trunk lines, including the trunk line 220 extending therebetween; while the distant exchange 50 and the P. A. B. X. 30 are interconnected by a group of two-way toll lines, including the toll line 226 extending therebetween.

The central oice 20, the I. B. X. 40 and the distant exchange 50 respectively comprise an operator position 20|, an operator position 2|1 and a toll operator position 225; while the P. A. B. X. 30 comprises an automatic dial switchboard provided with a number of operator positions, including the first operator position 30|. Each trunk line in the group extending from the central office 20 to the P. A. B. X. 30 terminates at the operator position 20| in the central office 20 and in a trunk circuit in the P. A. B. X. 30, the trunk line 203 terminating in the trunk circuit 205. Similarly, each trunk line in the group extending from the P. A. B. X. 30 to the central oflce 20 terminates in a repeater in the P. A. B. X. 30 and at the operator position 20| in the central oiice 20, the trunk line 202 terminating in the repeater 204. Also, each trunk line in the group extending between the I. B. X. 40 and the P. A.

B. X. 30 terminates at the operator position 2|'| in the I. B. X. 40 and in a trunk circuit in the P. A. B. X. 30,r the trunk line 220 terminating in the trunk circuit 22|. Finally, each toll line in the group extending between the distant exchange 50 and the P. A. B. X. 30 terminates at the toll operator position 225 in the distant exchange 50 and in a toll line circuit in the P. A B. X. 30, the toll line 226 terminating in the toll line circuit 221.

The I. B. X. 40 is provided with a switch train comprising a number of finder-connector links, including the finder-connector link 2| 6. Also, a telephone line having a line circuit individually associated therewith extends to each of the subscriber substations in the I. B. X. 4Q, the telephone lines 2|0 and 2|2 respectively extending to the subscriber substations TI and T2 and having the line circuits 2|| and 2|3 respectively associated therewith. Finally, a number .of trunk circuits are provided in the I. B. X. 40 which are individually associated with trunks terminating at the operator position 2|`| in the I. B. X. 4I), the trunk circuit 2|5 being individually associated with the trunk 2|4 terminating at the operator position 2|'|. It is noted that each finder-connector link in the I. B. X. 4D has access to each telephone line therein and to each trunk terminating at the operator position 2|'|.

The P. A. B. X. 32 is provided with a local switch train comprising a number of local finderselector links, including the local finder-selector link 235, and a number of local connectors, including the local connector 236. Also, telephone lines having line circuits individually associated therewith extend to each subscriber substation in the P. A. B. X. 30, the telephone lines 232 and 230 respectively extending to the subscriber substations T3 and T4 and having the line circuits 233 and 23| respectively associated therewith. A number of trunk circuits, including the trunk circuit 24|, is provided in the P. A. B. X. 36. It is noted that each of the local inder-selector links has access to each telephone line in the P. A. B. X. 30, to each local connector and to a number of trunks individually extending to the trunk circuits, including the trunk 24B individually extending to the trunk circuit 24|;

while each of the local connectors has access to each telephone line in the P. A. B. X. 38. v

Further, the P. A. B. X. 32 is provided with a toll switch train comprising a number of groups of switching links individually associated with the operator positions at the switchboard, one of the groups, including the switching link illustrated, being individually associated with the first operator position 32| at the switchboard. Each of the switching links comprises a finder and a first selector, the switching link illustrated respectively comprising the nder 309 and-the rst selector 50|). Also, it is noted that each of the switching links in the group, including the switching link illustrated, is commonly associated with the cable 322 extending to the rst f operator position 30|. Also, the toll switch train comprises a group of toll connectors, including the toll connector 54; a group of second selectors, including the second selector 505; and a group of delayed call selectors, including the delayed call selector 5lil. Each switching link has individually associated therewith timer apparatus and tone apparatus, the timer apparatus and the tone apparatus individually associated with the switching link illustrated being respectively indicated at 5H] and 6M. Further, a distributor 25B is provided, which is commonly associated with the Various operator positions at the switchboard and with the various trunk circuits and toll line circuits, for a purpose more fully explained hereinafter.

It is noted that each of the finders has access to a group of trunks individually extending to the group of trunk circuits, including the trunk circuit 225, this group including the trunk 20"! individually extending to the trunk circuit 295; to a group of trunks individually extending to the group of trunk circuits, including the trunk circuit 22|, this group including the trunk 222 individually extending to the trunk circuit 22|;l

. nel'.

to a group of trunks individually extendingV lto the group of toll line circuits, this group including the trunk 228 individually extending to the toll line circuit 221'; to a group of trunks individually extending to the group of trunk circuits, including the trunk circuit 24|, this group including the trunk 243 individually extending to the trunk circuit 24|; and to a group of trunks individually extending to the group of delayed call selectors, this group including the trunk 599 individually extending to the delayed call selector 51|). Similarly, each of the first selectors and each of the delayed call selectors has access to a group of trunks individually extending to the group of toll connectors, this group including the trunk 502 individually extending to the toll connector 534; and to a group of trunks individually extending to the group of second selectors, this group including the trunk 5133 individually extending to the second selector 525. Each of the toll connectors has access to a group of trunks individually extending to the group of repeaters, this group including the trunk 5M individually extending to the repeater 204; to a group of trunks individually extending to the group of trunk circuits, including the trunk circuit 22|, this group including the trunk 506 individually extending to the trunk circuit 22| and to a group of trunks individually extending to the group of toll line circuits, this group including the trunk 597| individually extending to the toll line circuit 221. Finally, each of the second selectors has access to a group of trunks individually extending to the group of local connectors, this group including the trunk 562 individually extending to the local connector 236.

The operator position 20| in the central oiilce 20, as best shown in Fig. 2, the operator position 2|? in the I. B. X. 4G, as best shown in Fig. 2, and the toll operator position 225 in the distant exchange 52, as best shown in Fig. 2, are connected and arranged in a conventional manner. Also, the subscriber substations T| and T2 in the I. B. X. 42, as best shown in Fig. 2, and the subscriber substations T3 and T4 in the P. A. B. X. 353, as best shown in Fig. 2, comprise conventional substation equipment; while the line circuits and trunk circuits respectively associated with the telephone lines and the trunks in the I. B. X. 4D, as best shown in Fig. 2, and the line circuits associated with the` telephone lines in the P. A. B. X. 32, as best shown in Fig. 2, are connected and arranged in a conventional man- Further, the nder-connector links in the I. B. X. 42, as best shown in Fig. 2, and the local finder-selector links and the local connectors in the P. A. B. X. 3&3, as best shown in Fig. 2, are connected and arranged in a conventional manner. Preferably, each of the finder-connector links comprises a finder and a connector of the well-known Strowger type; each of the local nder-selector links comprises a finder and a selector of the well-known Strowger type; and each of the local connectors is of the well-known Strowger type.

Preferably, each of the repeaters is identical to the repeater 234, shown in Fig. 2, which is connected and arranged in a conventional manner; each of the trunk circuits in the groups respectively including the trunk circuits 225, 22d and 24| is identical to the respective trunk circuits 235, 22| and 24|, shown in Fig. 2, which trunk circuits 22.5, 22E and 24| are respectively connected and arranged in manners substantially identical to the trunk circuits respectively shown in Figs. 4, 6 and 3 of the previously mentioned Voss and Crocker patent; and each of the toll line circuits is identical to the toll line circuit 221, shown in Fig. 2, which is connected and arranged in a .manner substantially identical to the toll line circuit shown in Fig, of the previously mentioned Voss and Crocker patent.

Preferably, the distributor 250, shown in Fig. 2, is connected and arranged in a manner substantially identical to the distributor shown in Fig. 20 of the previously mentioned Voss and Crocker patent; while each of the operator positions comprises apparatus identical to the first operator position 30|, shown in Fig. 3, which first operator position 30| comprises operator position equipment including la position circuit, position relays, position control keys, a position calling device, position digit keys, a receiver, a

transmitter, first and second sender links, and aV number of digit register senders, and which operator position equipment is connected and arranged in a manner substantially identical to the operator position equipment shown in Fig. 21,h part 1, part 2 and part 3, Fig. 22, part l and part 2, andFig. 23 of the previously mentioned Voss and Crocker patent.

Preferably, each of the first selectors is identical to the first selector 500, shown in Fig.A 5; each of the delayed call selectors is identical to the delayed call selector 510, shown in Fig. 5; each of the toll connectors is identical to the toll connector 504, shown in Fig. 5; and each of the second selectors is identical to the second selector 505, shown in Fig. 5; which first selector 500, delayed call selector 510, toll connector 504 and second selector 505 are respectively connected and arranged in a manner substantially identical to the first selector, the delayed call selector, the toll connector and the second selector, respectively, shown in Figs. 8, 9, and 18 of the previously mentioned Voss and Crocker patent.

Preferably, each of the iinders is identical to the nder 300, shown in Figs. 3 and 4, and comprises a switching mechanism 3I0 of the Strowger type, including a main wiper set provided with a number of wipers 3| I to 3 I 6, inclusive, and

capable of both vertical and rotary movements, and an associated main contact bank including ten vertical levels of contact sets arranged in circumferentially spaced-apart relationship. Also, the mechanism 3I0 includes a vertical control wiper SI1 capable of vertical movement and an associated vertical control contact bank. The mechanism 3I0 is provided with a vertical magnet M320 for moving the wiper set thereof in the vertical direction, a rotary magnet M3 I 8 for moving the Wiper set thereof in the rotary direction, anda release magnet M322 for releasing the wiper set thereof and for causing the wiper set to be returned to its normal position. Finally, the switching mechanism 3|0 has a number of sets of switch springs S323, S324 and S325 operatively associated therewith, which are controlled in accordance with the movements of the Wiper set thereof, in a manner more fully described subsequently.

Further, the finder 300 comprises a group of relays including a cut-through relay R330, a transfer relay R340, a step relay R350, a start relay R360, a talk relay R310, a toll relay R400, three supervisory relays R4|0, R420 and R425, and a cut-in relay R430, connected and arranged in a manner more fully described subsequently. Moreover, the iinder 300 has individually associated therewith a link listening or talk key K380 and a monitor key K440 which are operative to associate the nder 300 with the cable 302 extending to the first operator position 30 I. Finally, a busy lamp L326, a supervisory` lamp L321 and a hold lamp L409 are individually associated with the nder 300 for supervisory purposes.

Preferably, each of the timing apparatus is identical to the timing apparatus 5I0, shown in Fig. 5, which comprises a switch 5| I of the minor type, including three wipers 5|2, 5I3 and 5I4 provided with individually associated contact banks. Also, the minor switch 5II comprises a. rotary magnet M5I8 for driving the-wipers noted in the rotary direction and a release magnet M5I9 for releasing the Wipers noted and for causing them to be returned to their normal positions. Finally, a set of switch springs S5|5 is associated with the minor switch 5II which is controlled in accordance with the movements of the wipers thereof, in a manner more fully described subsequently. Further, the timing apparatus 5I0 comprises a group of relays, including a signal relay R520, a start relay R530 and three timer relays R540, R545 and R550, connected and arranged in a manner more fully described subsequently.

Preferably, each set of tone apparatus is identical to the tone apparatus 600, shown in Fig. 6, which comprises an amplifier including the thermionic discharge tube 680 having its input electrodes 683 and 684 arranged to be coupled to the tone condenser 614 through a coupling transformer 660, and provided with an output circuit comprising a resistance capacitance coupling network through which ampliedsignal voltages are impressed between the input electrodes 611 and 618 of the control tube 615. More specifically, the network coupling the input'electrodes of the control tube 615 with the output electrodes of the amplifier tube 680 comprises a coupling condenser 635 and a resistor 636. For the purpose of supplying energizing current to the lamentary cathode 618 ofA the control tube 615 and the cathode heater 685 of the amplifier tube 680, and for the additional purpose of providing anode and screen potentials for the tubes 615 and 680, a power pack is provided which comprises a power transformer 650, a full-wave rectifier tube .610 and a filter network including the series connected choke 640 and the shunt connected filter condensers 633 and 634. More specifically, the output circuit of the power pack includes the series connected circuit elements 640, 64I 644 and 645, anode potential being impressed upon the anode 616 of the control tube 615 through the Winding of the slow-to-release relay R6I5, and appropriate potentials being applied to the screen and anode electrodes 682 and 68| of the amplifier tube 680 through the impedance elements 643 and 642, respectively. The tone apparatus 600 also includes a group of relays including the above-mentioned tone relay R6|5, a start relay R6I0, a pair of control relays R620 and R625 and a switch relay R630. These relays are connected and arranged to operate in a manner more fully described hereinafter.

A better understanding of the connection and arrangement of the apparatus incorporated in the telephone system will be facilitated from a consideration of the detailed operation of the various pieces of apparatus incident to the handling of the various toll and trunk calls at the switchboard, as will appear hereinafter.

' Extension offcallsto the switchboard in thef P. A. B. X.

In order to extend a call from a subscriber substation, such as the subscriber substation Til; in the P. A. B. X. 30 to the switchboard therein; a call operation is rst performed at the calling subscriber substation T4, thereby to cause the line circuit 23| individually associated with the telephone line 230 extending to the subscriber substation T4 to operate. Upon operating, the line circuit 23| initiates operation of one of the local finder-selector links, such as the local lnder-selector link 235, in the local switch train, whereupon the local lnder-selector link 235 operates to seize the telephone line 230. When the telephone line 230 extending to the calling subscriber substation T is thus seized the line circuit 23| operates in order to mark the telephone line 230 as busy to the local connectors having access thereto; and the local finder-selector link 235 is rendered operative to a digit dialed thereinto. The subscriber at the subscriber substation T3 then dials a predetermined digit thereat,

thereby to cause the local :under-selector link 233 to operate and select an idle trunk in the associated group of trunks, such, for example, as the trunk 200 extending to the trunk circuit 20| When the trunk circuit 22| is thus seized it operates to mark the trunk 2633 extending thereto as a calling trunk in the Contact banks of the switchn ing links having access thereto, and to initiate operation, by way of the start conductor C232 has been previously prepared and that the rst operator position 30| has been preselected by the distributor 250, the distributor 230 operates to initiate operation'cf the nder 3000i the switching link illustrated. The finder 300 of the switching link illustrated operates in. order to seize the trunk 203 extending to the trunk circuit 23|, thereby to complete an obvious connectionv between the calling subscriber substation T3 and the first operator position 30|. The operator at the rst operator position 30| then answers, the

call and is informed by the subscriber at the, calling subscriber substation Tft concerning the eX- tension of the call, in the event this is necessary.

Subsequently, after the termination of the connection the switching link illustrated is released automatically or manually by theoperator at the rst operator position 30|, in a manner more fully explained hereinafter; whereupon the local finder-selector link 235 is released, assuming that the subscriber at the calling subscriber substation T4 has replaced the receiver of the telephone instrument thereat upon its associated switchhook at this time; and the line circuit 23| operates in order to mark the telephone line 230 extending to the subscriber substation Tl as idle to the local connectors having access thereto.

In order to extend a call from the central office 20 to the switchboard in the P. A. B. X. 30,

the operator at the operator position 20| in the central olice 20 first selects an idle trunk line,

in the group of trunk lines extending from the central oflice 20 to the P. A. B. X. 30, such as the trunk line 203, and then operates the apparatus atv the` operator position 20|, thereby to cause ringing current; to be projected over the trunk line 203. Theprojection of ringing current over, the trunk line 20:3 'intiates operationof the trunk circuit 205.` Upon operating, the trunk circuit 205 marks theftrunk 207 extending thereto as a calling trunk `in the contact banks -of the switche inglinks having access-thereto and initiates operation, by way of the start conductor C206 of the distributor 250; whereupon the distributor 250 operates to initiate yoperation of the nder or" a previously prepared one of the switching links at a preselected one of the operator positions at the switchboard. Assuming that the switching link illustrated, individually associated with the rst operator position 30| at the switchboard, has been previously prepared and that the rst operator position 30| has been preselected by thedstributorv 250, the,l distributor 250 operates to initiate operation offthennder 300 of the switching link illustrated. The nder 300 of the switching link illustrated operates in orderto seize the trunk 201 extendingto thetrunkcircuit 205,- thereby to complete an obvious connection between the operator position 20| in the l centrall office20 and the rst operator position I1. more. fully explained hereinafter, whereupon the trunk line203 extending; from the Central oflice 20toAA the P. A. B. X. 30is rendered idle, assuming that the operator at the operator position 20| inthe central oice 20. has disconnected from the trunk line 203 at this time.

In ,order to extend a call from the I..B. X. 404

to asa calling trunk inthe contact banks of the'.

switching links having access thereto, marks the trunk 306 extending thereto as busy to the toll connectors having access thereto, and initiates operation, by way of the start conductor C223 of the distributor 250; whereupon'the distributor 2501A operates to initiate operation of the nder of a previously prepared one of the switching links at a preselected onefof the operator positions at the switchboard. Assuming that the switching linkillustrated, individually associated with the rst operator position 30| at the switchboard, has been previously prepared and that theiirstloperatorY position 30| has been preselected by the-v distributor 250, the distributor 250 operates to initiate `operation ofthe finder 300 -of theswitchingV link illustrated. The finder 300 of the switching link illustrated operatesY in 'order to seize; the trunk 222 extendingi to the: trunk circuit 22|, thereby to complete anobvious connection betweenthe operator position 2|`| ,in the I. B. X. S0 and the lirst operator position: 30|. Theioperator--at -the rst operator'position 30| then an- When a connection is established at the` Vswers the call andl istinformed by the operator at the operator' position 2|1 coneerningthe extension of the call in the event this is necessary.

Subsequently, after the terminationV of the connection the switchinglinkillustrated isreleased automatically or manually bythe operator yat the rst operator position 30|', ina manner more fully explained hereinafter; whereupon the trunk line 220 extendingbetween the I. B. X. 40 and the P. A. B. X: 30 is rendered idle, assuming that the operator at the operator position 2|1 in the I. B. X. 40 has disconnected from the trunk line 220 at this time. The trunk circuit 22| then operates order to mark the trunk 506 extend: ing thereto as idle to theltoll connectors having access thereto.

In order to extend a callV from the distant exchange 50 to the switchboard in the PQA. B. X.

`30, the operator at the toll operator position 225 in the distant exchange 50 rst selects an idle toll line in the group of toll` lines extending between the distant exchange 50-and the P. A. B. X. 30, such as the toll line 226, and then operates the apparatus at the toll operator position 225, thereby to cause ringing current to be projected over the toll line 226.A The projection or'A ringing cur rent over the toll'line 226 initiatesvoperation of the toll line circuit 221. Upon operating, the toll` line circuit 221 marks the trunk 228V extending thereto as a calling trunk in, the contact banks of the switching links having access thereto; marks the trunk 501 extending thereto as busy to the toll connectors having access thereto; andv initiates operation, by way of the start conductor C229 of the distributor 250; whereupon the distributor 25|)l operates to initiate operation of the nder of a previously prepared one of the switching links at a preselected one ofthe operator positions at .the switchboard. Assuming that the switching link illustrated, individually 'associated with the first operator position 30| at the switchboard, hasbeen previouslyr prepared and that the rst operator position 30| has been preselected by the distributor 250, the distributor 250 operates to initiate operation of the finder 300 of the switching link illustrated. The finder 300 of vthe switching link illustrated operates in order to seize the trunk 228 extending tothe toll line circuit- 221, Vthereby to complete an obvious connection between the toll operator position 225 in the distant exchange 50 and theflrst operator. position 30|. The operator at the rst operator position 30| then answers the call and isinformed by the operator at the toll operator position 225 concerning the extension of the call, z

in the event this is necessary..

Subsequently, after the termination of the connection the switching link illustrated is released automatically .or manually by thecperator at l the first operator position 30|, in a manner more Extension of calls from the switchboard in the P. A. B.X.

In order to extend a call from one of the operator positions, such-astherst operator position 30|, at the 'switchboard in the P. A. B. X.!3!3V which has` been previously' answered' on one of the switching links associated therewith, such as the switching link illustrated, the operator at the first operator position 30| iirst operates the position digit keys thereat, thereby to cause one or more digits .corresponding to the route over which the call is to be extended to be registered in the associated digit register sender apparatus. The digit register sender apparatus then operates in order to cause the digits registered to be transmitted to the rst selector 500 of the switching link illustrated.

Assuming that the call is to be extended to a subscriber substation, substation T3, in the P. A. B. X. 30, the rst selector 500 operates to seize a trunk extending to an idle second selector, such as the trunk 503 extending to the second selector 505. The second selector 505 then operates in order to seive a trunk extending to an idle local connector, such as the trunk 508, extending to the local connector 236. rPhe local connector 236 then operates in order to select the telephone line 232 extending tothe called subscriber substation T3. The local connector 236 then operates to test'the idle or busy condition of the selected subscriber line 232, in accordance with conventional practice. The subsequent operation of the local connector 236 depends upon the idle or busy condition of the subscriber line 232 extending to the called subscriber substation T3. In the event the called subscriber substation T3 is idle at this time, ringing current is projected from the `local connector overthe subscriber line 232 to the called subscriber substation T3 in order to operate the ringer thereat; while ring-back tone current is returned over the trunk 508 the second selector 505, the trunk 503 and the first selector 500 to the finder'300, and thereover tothe calling connection. On the other hand, .in the event the called subscriber substation T3 is busy at this time, busy tone current is returned over the kpreviously traced connection to the finder 300 and thereover to the calling connection. Assuming that the called subscriber substation T3 is idle vat this time, the line circuit 233 associated with'the telephone line 232 extending thereto operates incident to seizure of the telephone line 232 by the local connector 236 in order to mark the telephone line 232 as busy to the other local connectors having access thereto.

VAt this point, it is noted that the operator at the iirst operator position 30| disconnects the link illustrated from the first operator position after operating the position digit keys when the connection is extended to a subscriber substationin the P.y A. B. X. 30. Further, it is noted that, in the event the called subscribed substation T3' is busy, the busy tone current returned from the localconnector 236 over thepreviously traced connection to the finder 300.is not only returned ,therefrom to the calling connection, but this busy tone current returned to the iinder 300 initiates operation of thetone apparatus 600 in order to cause flashing of the hold lamp L40!! associated with the link illustrated at the first operator position 30|, in a manner more fully explained hereinafter.

Subsequent to the termination of the connec tion the switching link illustrated is automatically released. When the switching link illustrated is thus released the second selector 505 and the local connector 236are released; where-- upon the line circuit 233 is operated in order to mark the telephone line 232 as idle to the local` such as the subscriber connectors having access thereto, assuming that the subscriber at the subscriber substation T3 has replaced the receiver of the telephone instrument thereat upon its associated switchhook at this time.

Assuming that the call is to be extended to the centra1 oiice 20, the iirst selector 5M `Operates to seize a trunk extending to an idle toll connector, such as the trunk 562 extending to the toll connector 524. The toll connector 504 then operates to seize a trunk extending to an idle repeater, such as the trunk 503| extending to the repeater 20d.

At this point, it is noted that the operator at the first operator position 33| retains the connection between the first operator position 30| and the link illustrated when a connection is extended to the central o-fce 2B. Accordingly, after the toll connector 52d seizes the trunk 56| extending yto the repeater 261i, the operator at the rst operator position operates the position apparatus thereat, thereby to cause ringing current to vbe projected over the trunk 50|, the repeater 26d. and the trunk line 202 to thel op,- erator position 2.9i in the central oiiice 20. The

projection of ringing current over the trunk line 262 extending from the P. A. B. X. 3E to the centrai office causes apparatus at the operator position 2M in the central oiiice 2t to be operated in order to indicate to the operator thereat that a call is extended to the operator position Zilli. r"he operator at the operator position 2B! then answers the call and is advised by the operator at the first voperator position 39| concerning the further extension of the call. The `operator at the rst operator position SSE then disconnects the link illustrated from the iirst operator position.

Subsequent to the termination of the connection, the operator at the iirst operator position Sti again connects the switching link illustrated to the first operator position 363| and'then operates-the position apparatus thereat, thereby to cause the release of this switching link.V When the switching link illustrated is thus released the trunkV line 232 is rendered idle, assuming that the operator at the operator position 2| in the central oiiice 2t has disconnectecltherefrom atA this time.

Assuming that the call is to be extended to the I. B. X. di), the rst selector 52) operates to seize a trunk extending to an idle toll connector, such as the trunk 5532 extending to the toll connector BEM. The toll connector 5M then operates to seize a trunk extending to an idle trunk circuit, such as the trunk 556, extending to the trunk circuit 22 l.

At this point, it is noted that the operator at the iirst operator position 32| retains the connection between the first operator position 30| and the link illustrated when a connection is eX- tended to the I. BX. di). Accordingly, after the toll connector Eiifi seizes the trunk 596 extending to the trunk circuit 22|, the operator at the first operator position 33| operates the position apparatus thereat, thereby to cause ringing current to be projected over the trunk 596, the trunk circuit 22| and the trunk line 22D to the operator position 2H in the'I. B. X. t0. The projection of ringing current over the trunk line 22|! extending between the P. A. B. X. 36 and the I. B. X. 40 causes apparatus at the operator position 2|? in the I. B. X. @it to ber operated in order to indicate to the operator thereat that a call is extended to the operator position 2|'|.

The operator at the operator position 2|'| then answers thecall and is, advised by the operator at the first operator position IHN` concerning the further extension of the call. The operator at the first operator position Stil then disconnects -the linkl illustrated from the first operator position 30|.

Subsequent to the termination of the connection, the operator at the rst operator position the distant exchange Eil, thefirst selector 52@ operates to seize a trunk extending to an idle 'tolli connector, such as the trunk 5W extendingy to the toll connector 504i. The toll connector 56e then operates to seize a trunk extending to an f idle toll line circuit, such as the trunk 587 extending to the toll line circuit 227. y At this point, it is noted that the operator at the first operator position St; i retains the connec-y tion between the first operator position 3li| and the link illustrated when a connection is extended to the distant exchange 56. Accordingly, after the toll connector 534i seizes the trunk 591. extending to the toll line circuit 227, the operator at the rst operator position 3M operates the position apparatus thereat, thereby to causel ringing current to4 be projected over the trunk 581, the toll line, circuit 22'! and the toll line 226 to the toll operator position 225l in thedistant exchange 50. The projection oi ringing current over the` toll line 22d extending between the P. A. B. X. 30 and the distant exchange 5G causes apparatus at the toll operator position 225 in the distant exchange 5t to be operated in order to indicate to the operator thereat that a call is extended to the toll operator position 225. The operator at the toll operator position 225 then answers the call and is advised by the operator at the rst operator position 33| concerning the further extension of the call. The operator at the first operator position 38| then disconnects the link-illustrated from the rst op-V erator position.

Subsequent to the termination ofV the connection, the operator at the rst operator position 32| again connects the switching link illustrated to the first operator position 36| and then operates the position apparatus thereat, thereby to cause the release of this switching link. When the switching link ilustrated is thus released the toll connector 5M is released; whereupon the toll line 226 is rendered idle, assuming that the' v operator at the toll operator position 225 in the distant exchange 5@ has disconnected therefrom at this time.

Detailed operation of the finder of a switching Zink to extend a caZZ to the associated operator position at the switchboard in the P. A. B. X.

When the operator-at any one of the operator positions, such as the iirst operator position 32|, at the switchboard in the P. A. B. X. tt is not engaged, she selects an idle one of the associated switching links, such as the switching link illustrated, and prepares it for use. The operator at Assuming Vthat .the call is to beV extended to the rst operator positionf30| prepares the switching link illustrated for use by operating the talk key K380 thereof,'this switching link being designated as idle by the extinguished' condition of the busy lamp L326. When the talk key Y K380 is thus operated a circuit is completed, at the contacts 383 thereof, for energizing the upper winding of the talk relay R310, this circuit including the grounded preparatory conductorV C306, whereupon the previously mentioned circuit for energizing the upper winding of the talk relay R310 is interrupted. Thus, it will be understood that the operation of the talk relay R310 in the switching link illustrated is effective to prevent the operation of the talk relay in any of the other switching links associated with the rst operator position 30|. Hence, the operation of the talk key K380 of the switching link illustrated is eiective to connect this switching link to the cable 302 extending to the first operator position 30| andV to prevent any of, the other switchinglinks associated with the cable' 302 from being connected thereto at this time.

Also, when the previously mentioned holding circuit for energizing the lower winding of the talk relay R310 is completed, the position equipment at the first operator position 30|',is rendered effective to answer a call routedthereto by Way of the switching link illustrated and the distributor 250 is controlled, thereby to mark the rst operator position 30| Vas selectable thereto; whereupon the distributor 250 selects the first operator position 30| in due course, the distributor 250 being operative automatically to select the ones of the operator positions at the switchboard marked as selectable thereto, in a predetermined order. l

Also, the talk relay R310 prepares, at the contacts 312', a circuit traced hereinafter for energizing the lower winding of the start relay R360. this circuit including'the start conductor `C3|3| extending by way of the cable 302, the position equipment at the rst operator position 30| and the cable 238 to the distributor 250. Further, the talk relay R310 interrupts,'at the contacts i313 and 315, a partially prepared connection,`

vtraced hereinafter, between the nnder 300 and the first selector 500, prepares, at the contacts 312 and 315, a connection, traced hereinafter.

'between thender 300 and the rst operator position 30|, and prepares, at the contacts 31| and 314, a connection, traced hereinafter, between Vthe first selector 500 and the first operator po- Further, the talk relay R310 intersition-30|. rupts,` at the contacts 311, a multiple circuit,

traced hereinafter, for illuminating `the busyv switching link illustrated to be seized bythe register sender apparatus at the first operator position 30|, prepares, at the contacts 310, a path including the release answer conductor C383, traced hereinafter, forshort-circuiting the upper winding of the start relay R360, and prepares, at the contacts 31 I', a circuit including the release'call conductor C382, traced hereinafter, for short-circuiting'the winding of4 the cut-in relay R430. l *When a` call arrives atthe switchboard, operation of the distributor 250 is initiated, as previously explained, whereupon ground potential therein is applied by way of the cable 238 and the position equipment at the rst operator position 30| to the start conductork C38| in the cable 302, assuming that the distributor 250 has selected.y the rst operator position 30| at this time. The application of ground potential to the start conductor C38| completes the previously mentioned circuit for energizing the lower winding of the start relay R360, this circuit extending from the grounded start conductor C38I by way of the contacts 312', the set of switch springs C325V and the lower winding of R360 to battery. When thus energized the start relay R360 operates to complete, at the contacts 36|, an obvious circuit for illuminating thebusy lamp L326, the illumination of the Abusy lamp L326 designating the switching link illustrated as busy. Also, the start relay R360 prepares, at the contacts 362, a vholding circuit, traced hereinafter, for energizing the upper winding thereof, and completes, at the contacts 363, an obvious path for applying ground potential to the hold conductor C389. Finally, the start relay R350 completes, at the contacts 365, an obvious holding circuit, including the set of switch springs S323 and the grounded start conductor 038|, for energizing the lower winding thereof'.

The application of ground potential to the hold conductor C389 completes an obvious circuit yfor illuminating the hold lamp L409 and an obvious multiple circuit for energizing the lower winding of the cut-through relay R330. When the lower winding of the cut-through relay R330 is thus energized this relay is rendered exceedrection and to complete, at the contacts 32|, an

obvious circuit for energizing the winding of the step relay R350. When thus energized the step relay R350 operates to interrupt, at the contacts 352, the previously traced circuit for energizing the vertical magnet M320, thereby to cause the vertical magnet M320 to restore. Upon restoring, the vertical magnet M320 interrupts, at the contacts 32|, the previously mentioned circuit for energizing 'the winding of the step relay R350, thereby to `cause the latter relay to restore and recomplete, at the contacts 352, the previously traced circuit for energizing the vertical magnet M320. The vertical magnet M320 and the step relay R350 interact in the manner described above, therebyto drive the wiper carriage of the Strowger mechanism 3|0 step by step in the vertical direction until the level in the associated main contact bank` terminating the ,calling trunk is reached, whereupon a circuit is completed for energizing the lower winding of the transfer relay R340. The circuit for energizing the lower g 3H by way of the contacts 343, the lowerv winding of R340, the contacts 35| and 345 and the vertical magnet M323 to battery. When this series circuit is completed the vertical magnet M320 remains in its operated position, thereby to retain the step relay R350 in its operated position; and shortly thereafter the transfer relay R340 operates, this relay being of the slow-tooperate type. Upon operating, the transfer relay R340 completes, at the contacts 332, an obvious circuit, in-cluding the contacts 33? and the grounded hold conductor C383, for energizing the upper winding thereof. Also, the transfer relay R340 interrupts, at the contacts 3M, a point in the previously mentioned circuit for illuminating the identity lamp associated withv the calling trunk or toll line circuit, and interrupts, at the contacts 333 and 335, the previously traced 4circuit for energizing the lower winding thereof in series with the vertical magnet M323. The vertical magnet M323 then restores, thereby to interrupt, at th-e contacts 32 i, the previously mentioned circuit for energizing the Winding of the step relay R350, thereby to cause the latter relay to restore.

It is noted that, when the wiper carriage of the Strovvger mechanism 350 is driven one step in the vertical direction, the set of switch springs l S324 is actuated into engagement, thereby toprepar-e an obvious circuit for energizing the release magnet M323; `and the set of switch springs S325 is actuated into disengagement, thereby to interrupt a point in the previously traced original circuit for energizing the lower winding of the start relay R333. lZ-Iowever, the previously traced holding circuit for energizing the lower winding of the start relay R330 is complete-d at this time, as the set of switch springs S323 is actuated only in the event the wiper carriage of the Strowger mechanism 3i@ is driven eleven steps in the rotary direction away from its normal position.

Upon restoring, the step relay R353 completes; at the contacts 352, a circuit for energizing the rotary magnet M313, this circuit extending from the grounded hold conductor C333 by way of the -contacts 331, 352 and 340 and the rotary magnet M3IB to battery. When thus energized the rotary magnet M3! 8 .operates to drive the wiper carriage of the Strowger mechanism 3 lll one step in the rotary direction and to complete, at the contacts 3l9, an obvious circuit for energizing the winding ofthe step relay R350, thereby to cause the latter relay to operate. Upon operating, the step relay R353 interrupts, at the contacts 352, the previously traced circuit for energizing the rotarymagnet MBit, thereby to cause the rotary magnet M3i8 to' restore and interrupt, at the contacts 35,9, the previously mentioned circuit for energizing the winding of the step relay R350. Thestep relay R350 then restores to recomplete, at the contacts 352, the previously traced circuit for energizing the rotary magnet M3 l 3. The rotary magnet M3! 3 and the step relay R355 interact, in the manner described above, in order to cause the wiper carriage of the Strowger mechanism 310 to-be driven step by step in the rotarydirectionr until the position of the calling trunk in the associated main f contact bank is reached, whereupon a circuit is completed for energizing the upper winding oi' the cut-through relay R330.

The circuit for energizing the upper winding of the cut-through relay R330 extends from 'the grounded hold conductor C383 by way of the upper winding of R333, the control wiper 3| 6 and the engaged contact in the associated main contact bank having battery potential thereon.

' When thus energized the cut-through relay R330 operates to complete, at the contacts 335, an obvious holding circuit, including the grounded hold conductor C333, for energizingthe intermediate winding thereof. Also, the cut-through relay R333 completes, at the contacts 336, an obvious path, including the grounded hold oonductor C383, for applying direct ground potential to the control wiper 313, thereby to cause the trunk or toll line circuit associated with the trunk seized by the wiper carriage of the Strowger mechanism 3H! to switchv through. Also, the cut-through relay R330linterrupts, at the contacts 33T, the previously traced circuit for energizing the rotary magnet lVi3i8, thereby to cause the rotary magnet M3i8 to restore, Whereupon further operation thereofV is arrested. Upon restoring, `rthe rotary magnet M3i8 interrupts, at the contacts 3&3, the previously mention'edk circuit for energizing the winding of the step relay R350, thereby to cause the latter relay to restore. Further, the cut-through relay R330 interrupts, at the contacts 337, the previously traced holding circuit for energizing the upper winding of the transfer relay R340, thereby to cause the latter relay to restore. Upon restoring, the transfer relay R330 completes, at the contacts 3M, an obvious path, including the contacts 373, `for applying ground potential to the identity wiper 3M, thereby to cause the identity lamp associated with the trunk or toll line circuit seized by the wiper carriage of the yStrowger mechanism 3I0 to be illminated. The illumination of the identity lamp` associated with Further, the cut-through relay R333 com-l pletes, at the contacts 330, the previously mentioned holding circuit for energizing the upper winding of the `start relay R350, this circuit extending irom ground by way of the contacts 334 and 352, the upper Winding of R350, C565 and the resistor 323 tov battery. Further, the cutthrough relay R333 completes, at the contacts 313i and 332, a connection between the seized trunk and the rst operator position 33|,this connection extending from the two line conductors of the seized trunk by Way oi the line wipers 35 l and 3i2 of the wiper carriage of the Strowger mechanism 3N, the contacts 33E, 332 and 312, 37H5 to the answer conductors C337 and C385, respectively, in the cable 302 extending to the rst operator position 3M.

calling trunk and the rst operator position 30|, whereupon the position apparatus at the rst operator position 30! operates to transmit a seizure tone to the receiver thereat in order to indicate to the operator at the rst operator position Accordingly, at this time,- an operative connection is completed between the y sender apparatus.

In this event, the trunk circuit seized by the wiper carriage of the Strowger mechanism 3|8 comprises a grounded discrimination lead connected to the contact in the main contact bank engaged by the discrimination wiper 3|3V of the wiper carriage of the Strowger mechanism 3|0, whereupon ground potential is applied to the discrimination conductor C513, as previously eX- plained. The application of ground potential to the discrimination conductor C513 is eiective to cause class recording apparatus in lector 500 to operate.

, Also, it is noted'that, when the previously mentioned connection between the calling trunk and the rst operator position `30| is completed, the position equipment at the first operator position 30| operates in order Yto cause operation vof the registersender apparatus to beinitiatedwhereupon the register sender apparatus is automatically. associated with the switching link illustrated, the switching link illustrated being marked for association with the register sender apparatus due to the presence Tof battery potential upon `the marking conductor C384 in the cable 302 extending to the rst operator position 30|. The path for applying battery potential the rst seto the marking conductor C384 extends from y Detailedv operation of the first selectm` of a switching link to extend a call from. the associated operator position at the switchboard 'in By Way of example,the operation of the first selector 500 of the switching link illustrated-at the first operator position 30| at the switchboard to extend a call from the rst operator position 30| will be continued. v'I'he operator at the rst operator position 30| now operates the digit keys included in the` position equipment thereat, whereupon digits are-registered in the register The digits registered in the digit register sender apparatus at the first operator position v30| are transmitted .by way of theline conductors C51| and C512 into the first selector 500, thereby to cause operation thereof in 'accordance with conventional practice.

In `the event the call is extended' to the central oflice 20,` the I. B. X., 40 or the P. A. B. X. 30, itis routed by way of one of the toll connectors, such" as the toll connector 504, as previously noted, and the operator atjtheflrst operator position 30| retains the connection to theswitching link illustrated by retaining the talk key K380 in` 'its operated position. In this event, when the first selector 500 seizes the trunk502 extending to the toll connector 504, an obvious circuit is completed for energizing the winding of the toll relay R400, thereby to cause the latter relay to operate. Upon operating, the toll relay R400 completes, at the contacts 402, an obvious multiple circuit for illuminating the busy lamp L326 and an obvious-multiple circuit for energizing the upper winding of the vsupervisory relay R425. However, this relay does not operate at this time, as itisv of the differential type. Further, the toll relay R400 interrupts, at the contacts 403, a point in a path traced hereinafter for applying ground potential to the start conductor C563 extending into the timer apparatus 5|0, thereby to prevent operation of the timer apparatus 5|0 at this time. Also, the toll relay R400 interrupts, at the contacts 40|, a point in a circuit traced hereinafter for energizing the windings of the supervisory relays R4|0 and R420, thereby to prevent operation thereof at this time. Further, the toll relay R400 completes, at the contacts 404, a multiple circuit, including the resistor 401, with the previously traced holding circuit for energizing the upper winding of the start relay R360. Whenthis multiple circuit is completed, the upper winding ofthe start relay R360 is partially deenergized. However, the latter relay remains in its operated position at this time and is rendered fast to release under the control of the operator at the rst operator position 30|, in a manner morel fully explained subsequently. Finally, the toll relay'R400 prepares, at the contacts 405, a point in. a circuit traced hereinafter for illuminating the supervisory lamp L321.

When all of the digits registered in the digit register sender apparatus in the position equipment at the first operator position 30| have been transmitted to the `first selector 500, the digit register sender apparatus operates to cause ground potential to be applied to the cut-in conductor C308 in the cable'302.'y This application of ground potential to the cut-in conductor C308 completes an obvious circuit, including the contacts 438 and the resistor 408, for energizing the winding of the cut-in relay R430, thereby to cause the latter relay to operate. Upon operating, the cut-in relay R430 completes, at the contacts 431, an obvious holdingv circuit, including the grounded hold conductor C389 and the resistor v408, for energizing the winding thereof. Further, the cut-in relay R430 interrupts, at the contacts 438, the'previously. traced original circuit for energizing the winding thereof, including the cut-in` conductor C308 in the cable 302. Further, the cut-in relay R430 interrupts, at the' contacts `436, the previously traced circuit for illuminating the hold lamp L409. The extinguishment of the hold lamp L409 indicates to the operator at the first operator position 30| nat all of the digits registered in the digit register sender apparatus have'V been transmitted and that theconnection has been extended by way of the first selector 500.

Also, the cut-in relay R430 interrupts, at the contacts 434, the previously traced path for applying battery potential in the rst selector 500 to the marking conductor C384 in the cable 302,-thereby to cause `the digit registersender apparatus in the position equipment at the first operator 'position 30| to be released. Further,

the cut-in relay R430 completes, at the contacts 435, an obvious path for applying ground potential to the hold conductor C514 extending into the rst selector 500, thereby to retain the first selector 500 and the toll connector 504 in their operated positions. Further, the cut-in relay R430 completes, at the contacts 43| and 432, a` connection between the rst selector 500 and the first operator position this connection extending from the rst selector by way of the line conductors 051| and C512, the contacts 3| and 432, the condenser 450 and the lower winding of the supervisory relay R425 in multiple, the line conductors C444 and C445 and the contacts 31| and 314 to the call conductors C388 and C336 in the cable 302 extending to the first operator position 313|. Also, it is noted that the lower winding of the supervisory relay R425 is bridged by the condenser 45|), thereby to provide a connection between the first operator position 39| and the rst selector 50B, excluding the lower winding of the supervisory relay R425, for' the transmission of signal currents. Further, the connection extends from the rst selector llll by way of the trunk 582, the toll connector 5M and one of the trunks to one of thev trunk circuits or to one of the toll line circuits. At this point, it is noted that the connection between the rst operator position 30| and the trunk circuit or toll line circuit comprises a dry loop, whereby the lower winding of the supervisory relay R425 is not energized.

Upon observing the extinguishment of the hold lamp LMS, the operator at the rst operator position 39| momentarily operates the position ring key in the position equipment at the iirst operator position 30|, thereby to cause ringing current to be projected over the called connection to the operator position involved therein. After the operator at the operator position involved in the called connection answersv the call the operator at the rst operator position 31N advisesV her concerning the further extension of the call and then disconnects the switching link illustrated from the first operator position 3ll|y by returning the talk key K38li to its normal position, whereupon a direct connection is completed by way of the switching link illustrated between the calling connection and the called connection.

When the talk key E380 is returned toits normal position there is interrupted, at the contacts SM thereof, the previously traced holding circuit for energizing the lower winding of the talkY relay R310, including the hold conductor C395, thereby to cause the talk relay R316v to restore. Upon restoring, the talk relay R315 interrupts, at the contacts 313', a point in the previously traced holding circuit for energizing the lower winding thereof, whereupon the position relays in the position equipment at the first operator position 3o! operate in order to cause ground potential to be reconnected to the preparatory conductor Cflt; whereupon the talk keys of the other switching links associated with the lirst operator position 3| are rendered operative to connect the other switching links to the iirst operator position Bill. Further, the talk relay R319 interrupts, at the contacts 312', a further point in the previously traced circuit for energizing the lower winding of the start relay Rte, interrupts, at the contacts 31V, a further point in the previously mentioned path for short-circuiting the winding of the cut-in relay R439, including the release call conductor C332, and interrupts, at the contacts Slt, a further point in the previously mentioned path for short-circuiting the upper winding of the start relay RBE, including the release answer conductor C383. terrupts, at the contacts 319, a further point in the previously mentioned connection between the marking conductor C384 in the cable 382 and Further, the talk relay R310 inthe hold conductor C'lll extending into the first selector 59|); and interrupts, at the contacts 318, the previously traced circuit for illuminating the identity lamp associated with the calling trunk tion between the finder 30|) and the answer conv ductors C381 and C385, interrupts, at the contacts 31| and 314, the connection between the iirst selector 50|? and the call conductors C388 and C336, and completes, at the contacts 313 and 3155, an obvious connection between the finder 365i and the rst selector 5W. At this time, a direct connection is completed by way of the switching link illustrated between the calling connection and the called connection.

On the other hand, in the event the call is extended to a local subscriber substation in the P. A. B. X. 38, it is routed by way of one of the second selectors, such as the second. selector 595, as previously noted; and the operator at the rst operator position 39| disconnects from the switching link illustrated by restoring the talk key K385i after all of the digits have been registered in the digit register sender apparatus. In this event, when the rst selector till) seizes the trunk 583 extending to the second selector 5&5, the previously mentioned circuit for energizing the winding of the toll relay R696 is not completed, thereby to prevent operation oi the latter relay at this time.

When the talk key H339 is returned to its normal position the talk relay R31@ restores, thereby to complete the previously traced connection between the finder 3B@ and the first selector Ello incident to the operation of the cutin relay Reti), in the manner previously eX- plained. When all of the digits registered in the digit register sender apparatus in the position equipment at the first operator position 39| have been transmitted, the cut-in relay Rll) operates, in the manner previously explained, thereby to complete the previously mentioned connection between the iinder Stil and the rst selector 553D. At this time, the connection is further extended from the first selector 5|l9 by way of the trunk 563 and theV second selector 565i to one of, `the local connectors in the local switch train, such as the localconnector 236. the second` selector 5&5 has seized the trunk 50.8 extending to the local connector and the local connector 23? has operated to select the called telephone line.

At this point, it is noted that the connection extending `between the trunk circuit or the toll line circuit seized by the wiper carriage of the Strowger mechanism 3H! and the local connector 236, and including the iinder .3i-ill, the rst selector 5.0M, the trunk 533, the second selector llfi and the trunk EES, is of the battery feed type, whereby the previously traced circuit for energizing the lower winding of the supervisory relay R625 is completed. However, the supervisory relay Ell-25 is not operated at this time as it is of the differential type, as previously noted. I

At this time, the local connector operates to test the idle or busy condition of the selected telephone line, whereupon either ring-back tone current or busy tone current is returned over Thus,

the previouslyA traced connection to the finder 300, in the manner previously explained.

Neglecting for the present the operation of the finder 300, in response to the ring-back tone current or busy tone current returned thereto, and assuming that the telephone line selected by the local connector 236 is idle and that the call is answered promptly, when the call is answered at the called subscriber substation associated with the telephone line seized by the local connector, the local connector 236 operates to reverse battery back over the previously traced connection, including the finder 300. When the battery is reversed back over the finder 300 the lower winding of the supervisory relay R425 `is energized in the same direction as the upper winding thereof, thereby to cause the latter relay to operate. Prior to operation of the supervisory relay R425 and incident to the operation of the cut-in relay R430, the previously mentioned path for applying ground` potential to the start conductor C563 extending into thev timer apparatus |0 is-completed, this path extending from ground by way of the contacts 36|, 311, 40|, 433, 421, 422 and 403 to the start conductor C563. The application of ground potential to the start conductor C563 extending into the timer apparatus 5|0 initiates operation thereof, in a manner more fully explained hereinafter. Upon operating, the supervisory relay R425 interrupts, at the contacts 421, the previously traced path for applying ground potential to the start conductor C563 extending into the timer apparatus 5|0, thereby to arrest further operation thereof at this time. Further, the supervisory relay R425 completes, at the contacts 426, a circuit substantially identical to that previously traced for energizing the winding of the supervisory relay R420, thereby to cause the latter relay to operate, for a purpose more fully explained hereinafter. At this time, an operative connection is completed between the calling connection and the called subscriber substation in the P. A. B. X. 30, including the switching link illustrated.

Supervision and release of the switching link at one of the operator positions at the switch board in the P. A. B. X.

Continuing now with the supervision of the switching link illustrated at the rst operator position at the switchboard in the P. A. B. X. 30, it is pointed out that, when a connection is extended thereover to either the central oce 20, the I. B. X. 40 or the distant exchange 50, both the calling connection and the called connection have supervision. In this event, when the attention of the operator at the first operator position 30| is desired by the party or operator associated with the calling connection, a control is performed over the calling connection, thereby to cause either the trunk circuit or the toll line circuit included in the calling connection to operate, whereupon ground potential is applied to the supervisory conductor engaged by the supervisory wiper 3|5 of the wiper carriage of the Strowger mechanism 3|0. This application of ground potential to the supervisory wiper v3|5 tion, a controlis-perforrried over the called connection, thereby to cause either the trunk circuit or the toll line circuit included in the called connection to operate and apply ground potential to the supervisory conductor C516 extending into the first selector 500. This application of ground potential to the supervisory conductor C516 completes an obviousV circuit, including the contacts 405 and 4|4 and the contacts 38| and 386 of the talk key X380 for illuminating the supervisory lamp L321.

The illumination of the supervisory lamp L321 indicates to the operator at the first operator position 30| thatV her attention is required in connection with a call routed by way of the switching link illustrated; whereupon the operator at the rst operator position 30| operates the talk key K380,'thereby to cause reoperation of the talk relay R310; whereupon the previously traced connection between the iirst operator position 30| and the switching link illustrated is recompleted.

Incident to theftermination of an established connection routed by way of the switching link illustrated between a calling connection and a called connection, including the central oice 20,

'the I. B. X. 40 or the distant exchange 50, controls are performed over the calling and called connections, thereby to complete the previously traced circuits for illuminating the supervisory lamp L321. The operator at the rst operator position 30| then reestablishes the connection between the rst loperator position 30| and the link illustrated byoperating the talk key X380. Upon discovering/that both the calling and the calledV connections have-'been terminated, the operator at the first operator position 30| releases the switching apparatus, including the switching link illustrated and the toll connector 504, by momentarily operating the release call and release answer keys in the position equipment at the first operator position 30|. When the release call and the release answer keys in the position equipment at the rst operator position 30| are momentarily operated, ground potential is momentarily connected to both the release call conductor C382 and the release answer conductor C383 in the cable 302 extending to the first operator position 30|. The application of ground potential to the release call conductor C382 in the cable 302 completes a path for shortcircuiting the winding of the cut-in relay R430, this path extending from the grounded release call conductor C382 by way of the contacts 31|', R430 and the contacts 431 to the grounded hold conductor C389. When the cut-in relay R430 is thus short-circuited it restores to interrupt, at the contacts 431, a further point in the previously traced path for short-circuiting the winding thereof. The application of ground potential to the release answer conductor C383 completes a path for short-circuiting the upper winding of the start relay R360, this path extending from the grounded release answer conductor C383 in the cable 302 by way of the contacts 310, C565, the upper winding of R360 and the contacts 362 and 334 to ground.v When the upper winding of the start relay R360 is thus short-circuited this relay restores.

Upon restoring, the cut-in relay R430 interrupts, at the contacts 435, the previously mentioned path for applying ground potential to the hold conductor C514 extending into the rst selector 500, thereby to cause the first selector 500 to be released. When the rst selector 500 riage of the Strowger mechanism 3|0 is released it is returned to its normal position, whereupon the set of switch springs S325 is actuated into engagement and the set of switch springs S324 is actuated into disengagement, thereby to interrupt the previously traced circuit for energizing the release magnet M322, whereupon the release magnet M322 restores. Also, the start relay R360 interrupts, at the contacts 353, the 'previously traced holding circuit for energizing the intermediate winding of the cut-in relay R330, 1

thereby to cause the latter relay to restore. Further, the start relay R360 interrupts, at the contacts 35 the previously mentioned circuit for illuminating the busy lamp L325. The extinguishment of the busy lamp L325 indicates to the operator at the first operator position 30| that the switching link illustrated is completely released.

After the operator at the rst operator position 30| momentarily operates the release call and release answer keys in the position equipment at the first operator position 30| she returns the talk key E350 to its normal position, thereby to interrupt the previously traced holding circuit for energizing the lower winding of the talk relay R370, whereupon the latter relay restores. When the switching link illustrated is thus released the previously traced circuits for illuminating the supervisory lamp L32'l `are interrupted, thereby to cause the supervisory lamp L321 to be extinguished. At this time, the apparatus involved in the established connection is completely released and the switching link i1- lustrated is available for further use.

In connection with the extension of a call by way of the switching link illustrated, the second selector 505 and the local connector 236 to a called subscriber substation in the P. A. B. X. 30, it is again noted that operation of the timer apparatus 5 0 is initiated. As previously pointed out, when the cut-in relay R530 in the iinder 300 operates, ground potential is applied to the start conductor C553 extending into the timer apparatus 5|0. This application of ground potential to the start conductor C553 completes a circuit for energizing the upper winding of the start relay R530, this circuit extending from the grounded start conductor C553 by way of the contacts 525 and the upper winding of R530, the contacts 535, 555 and 55| and the resistor 537 to battery. When thus energized the start relay R550 operates to complete, at the contacts 534, an obvious holding circuit substantially identical to that previously traced for energizing in series the upper and lower windings thereof. Also, the start relay R530 interrupts, at the contacts 535, the previously traced original circuit for energiding the upper winding thereof, and completes, at the contacts 533, an obvious circuit, including the contacts 553, for energizing the winding of the timer relay R540. When thus energized the timer relay R540 opcrates to set the weighted armature thereof into vibration, whereupon there is completed inter'- mittently, at the contacts 54|, an obvious circuit, including the contacts 533, for energizing the winding of the timer relay R545 in multiple with the resistor 535. It is noted that the timer relay R545 is of the slow-to-.operate type; and the circuit thereof is only intermittently come pleted, due to the vibration of the weighted armature cf the timer relay R540. Accordingly, there is a considerable time delay after the operation of the timer relay R540. After the time delay mentioned the timer relay R545 operates to complete, at the contacts 548, an obvious circuit for energizing the winding of the timer relay R550 in multiple with the resistor 538. Shortly after the timer relay R550 in thus energized it operates, this relay being of the slow-to-operate type. Upon operating, the timer relay R550 interrupts, at the contacts 553 the previously mentioned circuit for energizing the winding of the timer relay R540, thereby to cause the latter relay to restore. Upon restoring, the timer relay R540 interrupts, atthe contacts 55|, the previously traced circuit for energizing the winding of the timer relay R545, thereby to cause the later relay to restore shortly thereafter, the

winding of the timer relay R545 being short-circuited by the resistor 535. Upon restoring, the timer relay R555 interrupts, at the contacts 548, the previously mentioned circuit for energizing the winding of the timer relay R550, thereby to cause the latter relay to restore shortly theree after, the winding of the timer relay'R550 being short-circuited by the resistor 538. Upon ree storing, the timer relay R550 recompletes, at the contacts 553, the previously traced circuit for energizing the Winding of the timer relay R540, thereby to cause the latter relay of reoperate; whereupon a Anew cycle of operation of the timer relays R540, R545 and R550 is initiated.

While the timer relay R550 .occupies its `operated position, and when the timer relay R545 restores, it completes, at the contacts 541, a cir# cuit for energizing the rotary magnetV M5|8, this circuit extending from ground by way of the contacts 552, 541 and 53| and the rotary magnet M5|8 to battery. When thus energized the rotary magnet M5|8 operates, thereby to drive the wipers noted of the minor switch 5|| one step in the clockwise direction. Subsequently, when the timer relay R550 restores it interrupts, at the contacts 552,` the previously traced circuit for energizing the rotary magnet M5|8, thereby to cause the rotary magnet M5|8 to restore. In View Vof the above description of the cycle of operation ofthe timer relays R540, R545 and R550, it will be understood that, incident to the completion of each cycle thereof, the rotary magnet M5|B is operated; whereby the wipers noted of the minor switch 5H are driven step by step in the clockwise direction. When the wipers noted of the minor switch 5|! lare driven one step in the clockwise direction the set of switch springs S5|5 is actuated into engagement, thereby to prepare a circuit traced hereinafter for energizing the release magnet M519.

When the subscriber at the called subscriber substation answers the call the local connector 236 operates to reverse battery over the called connection to the nder 300, thereby to cause operation of the supervisory relay R425, as previously explained. Upon operating, theY supere visory relay R425 interrupts, at the contacts 421,- the previously 'traced path for applying ground the cycle of operation of the timer relays R540, R545 and R550. Also, the start relay R530 in-l terrupts, at the contacts 53|, the previously traced circuit for energizing the rotary magnet Ml8, thereby to arrest furtheroperation of the minor switch 5| I. Finally, the start relay R530 completes, at the contacts 532, the previously mentioned circuit, including the set of switch springs S5|5, for energizing the release magnet M5|9. When thus energized.thereleasemagnet M5|9 operates in order to release Athe wipers noted of the minor switch 5| whereupon they are returned to their normal positions. When the wipers noted of the minor switch 5| I are returned to their normal positions the `set of switch springs S5|5 is actuated int-o disengagement, thereby tc interrupt the previously traced circuit for energizing the release magnet M5|0 in order to cause the release magnet M5|9 to restore. At this time, the timer apparatus 5|0 is completely released.` a

In theevent the subscriber at the called subscriber substation in the P. A. B. X. `does not answer the call within a predetermined time interval, the supervisory relay R425 is not operated prior to the time that the wipers noted of the minor switch 5|| have been driven nine steps in the clockwise direction away from their normal positions. In this event, a circuit is completed for energizing the lower winding of the signal relay R520, this circuit extending from the grounded tenth contact engaged by the wiper 5|3 of the minor switch 5| kby way of C563', the contacts 523 and the lower winding of R520 to battery. When thus energized the signal relay R520 operates to complete, at the contacts 522, an obvious holding circuit, including the grounded start conductor C563, for energizing the upper winding thereof.4 Also, the signal relay R520 interrupts, at the contacts 523, thepreviously traced original circuit for energizing the lower winding thereof; and interrupts, at the contacts 524, the previously traced holding `circuit for energizing in series the upper and lower windings of the start relay R530, thereby to cause the start relay R530 to restore and release the minor switch 5|| and to arrest operation of the timer relays R540, R545 and R550, in a manner previously explained.V Finally, the signal relay R520 completes, at the contacts 52|, an obvious circuit, including the interrupter conductor C560, for Vintermittently illuminating the hold lamp L409, ground potential being applied to the interrupter conductor C560 at a rate of approximately sixty impulses per minute.

The flashing of the hold lamp L409 indicates to the operator at Vthe first operator position 30| that the connection has not been completed to the called subscriber substation in the P. A. B. X. 30. Accordingly, the operator at the nrst operator position 30| reoperates the talk key X380, thereby to cause reoperation of the talk relay R310. Upon operating, the talk relay R310 recompletes the previously traced connection between the switching link illustrated and the rst operator position 30|, and interrupts, at the contacts 311, the previously traced path for applying ground potential to the start conductor C563 extending into the timer apparatus 5|0, in order to interrupt the previously traced holding circuit for energizing the upper winding of the signal relay R520, whereupon the latter relay restores. Upon restoring, the signal relay R520 interrupts, at the contacts 52|, the previously traced circuit, including the interrupter conductor C560, for intermittently illuminating the hold lamp L409, thereby tok cause the hold lamp L409 to cease flashing. The operator at the rst operator position 30| then advises the calling party or operator over the calling connection that the desired connection to the called subscriber substation in the P. A. B. X. 30 may not be immediately had.

Continuing now with the supervision of the switching link illustrated at the first operator position v30| at the switchboard in the P. A. B. X. 30, it is pointed out that, when a connection is extended therecver to a called subscriber substation in the P. A. B. X. 30, both the calling connection and the called connection have supervision. In this event, when the attention of the operator at the rst operator position 30| is desired by the party or operator associated with the calling connection, `a control is performed over the calling connection, thereby to cause the supervisory lamp L321 to be illuminated, in the manner previously explained.

Also, in this event, when the attention of the operator at the rst operator position 30| is desired by the subscriber associated with the called connection, the subscriber at the called subscriber substation dials a predetermined digit. At this time, the supervisory relay R425 occupies its operated position, thereby to complete, at the contacts 426,` the Apreviously traced circuit for energizing the winding of the supervisory relay R420 in order to retain the latter relay in its operated position. When the predetermined digit mentioned is dialed the supervisory relay R425 operates and restores intermittently, thereby to complete, at the'contacts 421, a circuit for energizing the winding of the supervisory relay R4I0, this circuit extending from ground by way of the contacts 36|, 311, 40|, 433, 421 and 42| and R4|0 to battery. When thus energized the supervisory relay R4|0 operates to complete, at the contacts 4 3, an obvious holding circuit substantially identical to that previously traced for energizing the Winding thereof. Subsequently, when the supervisory relay R425 reoperates it completes, at the contacts 426, a circuit for illuminating the supervisory lamp L321, this circuit extending from ground byvway of the contacts 36|, 311, 40|, 433, 426 and 4|2, the contacts 386 of the talk key K380 and the supervisory lamp L321 to battery.

When the supervisory lamp L321 is thus illuminated the operator at the rst operator position 30| operates the talk key K380, thereby to cause operation of the talk relay R310, in the mannerv previously explained, whereupon the link illustratedis connected to the rst operator position 30|. Also, the talk relay R310 interrupts, at the contacts 311, the previously traced holding circuit for` energizing the winding of the supervisory relay R4|0, thereby to cause the iatter relay to restore, and interrupts, at the contacts 311, the previously traced circuit for illuminating the supervisory lamp L321.

Incident to the termination of an established connection routed by way of the switching link illustrated between a calling connection anda 

